Predicting Dinitrogen Activation via Transition‐Metal‐Involved [4+2] Cycloaddition Reaction

Abstract

As the strongest triple bond in nature, the N≡N triple bond activation has always been a challenging project in chemistry. On the other hand, since the award of the Nobel Prize in Chemistry in 1950, the Diels‐Alder reaction has served as a powerful and widely applied tool in the synthesis of natural products and new materials. However, the application of the Diels‐Alder reaction to dinitrogen activation remains less developed. Here we first demonstrate that a transition‐metal‐involved [4+2] Diels‐Alder cycloaddition reaction could be used to activate dinitrogen without an additional reductant by density functional theory calculations. Further study reveals that such a dinitrogen activation by 1‐metalla‐1,3‐dienes screened out from a series of transition metal complexes (38 species) according to the effects of metal center, ligand, and substituents can become favorable both thermodynamically (with an exergonicity of 28.2 kcal mol−1) and kinetically (with an activation energy as low as 13.8 kcal mol−1). Our findings highlight an important application of the Diels‐Alder reaction in dinitrogen activation, inviting experimental chemists’ verification.

Stepwise Reduction of Dinitrogen by a Uranium–Potassium Complex Yielding a U(VI)/U(IV) Tetranitride Cluster

“…This value is close to the isotopomer shift calculated from reduced mass considerations (923 cm –1 ). These values are higher than those reported for the U­(VI) terminal nitride complex [NU­(Tren TIPS )] (914 and 883 cm –1 for 14 N and 15 N, respectively) but lower than the value reported for the UN 2 formed in the gas phase (1051.0 cm –1 ) …”

“…Moreover, the secondary interactions of metal dinitrogen complexes with alkali ions are known to enhance the activity of the iron-based Haber–Bosch catalysts . Molecular complexes capable of effecting the cleavage of dinitrogen to nitrides ,, are essentially limited to d-block metals , and are all proposed to involve multimetallic intermediates , that have been isolated in a few instances. ,,, In particular, based on the structure of the final nitride complex, multimetallic cooperation of transition metals and Lewis acids, potassium in particular, has been suggested by several groups to be a crucial step in the six-electron dinitrogen cleavage to nitride involving alkali ions as reducing agents. ,,,, …”

A radical mechanism for C–H bond cross-coupling and N2activation catalysed by β-diketiminate iron complexes

“…In 2015, Holland and coworkers 12 developed a nitrogenase-inspired complex with a sulfur-rich coordination sphere, which could break the Fe-S bond and bind N 2 after reduction. In addition, some other transition metal catalysts, including cobalt, 13 chromium, 14 scandium, 15 and rhenium complexes, 16 and non-meta systems [17][18][19][20][21] have also been developed for catalytic NN bond activation. Braunschweig et al 22,23 reported binding and reduction of one or two N 2 molecules by a nonmetal dicoordinated borylene.…”

Theoretical Study on Reaction Mechanisms of Dinitrogen Activation and Coupling by Carbene‐Stabilized Borylenes in Comparison with Intramolecular C−H Bond Activation

“…Due to the advantage of the diversity of oxidation-state and orbital, transition metals have been used for N 2 activation and conversion into ammonia and other useful nitrogen compounds. [2][3][4][5][6][7][8][9][10][11][12][13][14] Note that the industrial Haber-Bosch process [15] for ammonia production requires relatively harsh conditions (350°to 500 °C and 150 to 200 atm), leading to consumption of more than 1% of the world's annual energy supply. Thus, developing main group systems as an alternative strategy for N 2 activation has attracted extensive attention in recent years.…”

“…The significant bond strength (bond dissociation energy: 945 kJ/mol) and HOMO‐LUMO gap (10.8 eV; HOMO: the highest occupied molecular orbital; LUMO: the lowest unoccupied molecular orbital) in dinitrogen (N 2 ) [1] make its activation particularly challenging. Due to the advantage of the diversity of oxidation‐state and orbital, transition metals have been used for N 2 activation and conversion into ammonia and other useful nitrogen compounds [2–14] . Note that the industrial Haber‐Bosch process [15] for ammonia production requires relatively harsh conditions (350° to 500 °C and 150 to 200 atm), leading to consumption of more than 1% of the world‘s annual energy supply.…”